# Adenosine Adenosine is a molecule that has a lot of complex functions in the body. The main function is controlling how sleepy we get. Adenosine builds during the day causing us to be sleepy at bedtime then decreases so we can wake up. When we wake up the body is not finished flushing adenosine. Caffeine binds to adenosine receptors blocking its function, however once caffeine wears off adenosine starts to surge again, causing sleepiness. This is why it's important to not drink caffeine for at least 90 minutes after waking.